Doses of oral vitamin C up to 3 grams can produce transient peak plasma concentrations two to threefold higher than 200 mg, returning to baseline after 24 hours.

“at 500 milligrams the bioavailability decreases and excess vitamin C gets extreme but that's not the end of the story even though bioavailability is diminished after 500 milligrams per day plasma levels still increase after higher oral doses up to 3 grams producing transient peak plasma concentrations that are two to threefold higher than those with 200 milligrams of oral vitamin C the plasma levels peak at around 220 micro moles per liter and return to baseline after 24 hours”